Hydraulic fracturing is a technique that is commonly used to enhance oil and gas production. In this process, a large amount of fluid is pumped into a drilled wellbore with targeted areas of the rock are exposed to the fluid. The high pressure fluid induces a crack or fracture in the rock. The hydraulic pressure and type of fracturing fluid system affects the size, depth and surface area of the fracture that allows for hydrocarbon production from the formation. Once the hydraulic pressure is removed, the fracture closes in a short period of time. In order to keep the fracture open to allow hydrocarbons to escape and be collected, particles called proppants are introduced into the well to “prop” open the fracture. Commonly used proppants are sand or ceramics. The amount of oil or gas produced from the fracture is highly dependent on the quantity and placement of the proppant in the fracture. Better proppant placement deeper into a well yields a longer effective fracture length, and thus better production. Therefore, in order to improve hydrocarbon yield from hydraulically fractured wells, any improvement in placement can have a large impact on production.
Hydraulic fracturing fluids can be water based, and such systems can be categorized broadly into 3 main classes: Polymer gels that are crosslinked with metal ions or non-metallic compounds such as borates form fracturing fluid with maximum viscosity to create wide fracture width and carry the proppant deep into the fractured matrix, polymer gels in which the polymer concentration is sufficient to create a substantial viscosity increase but is not crosslinked and a low concentration of polymer in the water to provide substantial reduction in friction pressure but minimal increase in viscosity to aid in proppant transport. This third class of fracturing fluid system is also known as “slick water”. Since most proppants are higher density than the fluids used to hydraulically fracture wells, particles settling out of the fluid suspension (rather than being carried further out in the fracture) can be a limiting factor in the effectiveness of the fracturing process. Proppant that settles out of the fluid prior to placement in a fracture is not only wasted; but can quickly contribute to the premature termination of the fracturing treatment. In addition, the proppant that settles in the near wellbore (or the widest part/base of the fracture) creates dunes which can further limit effective placement of the particles that remain in the suspension.
Proppant settling rate is affected by several factors; primary amongst these is the density of the particles relative to the fluid, the drag imparted on the particle surface as it flows through fluid and the viscosity of the fluid carrying the proppant.
Accordingly, there is a need to reduce proppant density to enhance transport. However, there are problems with prior methods and compositions for reducing proppant density. For example, proppant densities can be reduced by creating a porous proppant structure, by adding a coating so that the coated particle has a lower density than the carrier and/or that increases particle drag to reduce settling, or by attachment of gas bubbles to reduce the density of the bubble/particle aggregate. Engineering of materials to generate a low density porous proppant results in an expensive low density ceramic material or a very high cost thermoplastic material. Adding of coatings such as hydrogels to increase particle drag and reduce density have the disadvantage of high cost, complex processing, and the possibility of leaving a residue on the sand that can have a negative impact on well production due to clogging of pores with the hydrogel.
Generation of bubbles on the surface of the particles can be used to reduce density and increase transport. Nitrogen can be used as a component in energized fracturing systems and can be added as an additional component in a fracturing job. However, current chemistries for hydrophobic surface coating of proppant via addition of liquid ingredients such as frothers are quite complex and costly, and require the use of hazardous chemicals on the wellsite.
Thus there is a need for a simpler, less complex method and chemistry for preparation of a hydrophobic surface on a proppant to allow for enhanced transport via attachment of buoyant gas bubbles. The present embodiments satisfy these needs as well as other.